Magnetic domain walls in constrained geometries

Magnetic domain walls have been studied in micrometer-sized Fe20Ni80 elements containing geometrical constrictions by spin-polarized scanning electron microscopy and numerical simulations. By controlling the constriction dimensions, the wall width can be tailored and the wall type modified. In particular, the width of a 180 degree Neel wall can be strongly reduced or increased by the constriction geometry compared with the wall in unconstrained systems.Comment: 4 pages, 6 figure

Model study for the nonequlibrium magnetic domain structure during the growth of nanostructured ultrathin films

The nonequilibrium magnetic domain structure of growing ultrathin ferromagnetic films with a realistic atomic structure is studied as a function of coverage and temperature. We apply a kinetic Monte Carlo method to a micromagnetic model describing the transition from superparamagnetic islands at low coverages to a closed ferromagnetic film. The magnetic relaxation and the island growth happen simultaneously. Near the percolation threshold a metastable magnetic domain structure is obtained with an average domain area ranging between the area of individual magnetic islands and the area of the large domains observed for thicker ferromagnetic films. We conclude that this micro-domain structure is controlled and stabilized by the nonuniform atomic nanostructure of the ultrathin film, causing a random interaction between magnetic islands with varying sizes and shapes. The average domain area and domain roughness are determined. A maximum of the domain area and a minimum of the domain roughness are obtained as a function of the temperature.Comment: 19 pages, 4 Postscript figures; to be published in J. Magn. Magn. Mater., accepted (2001); completely revised manuscrip

Use of a Granulocyte Immunofluorescence Assay Designed for Humans for Detection of Antineutrophil Cytoplasmic Antibodies in Dogs with Chronic Enteropathies

Perinuclear antineutrophil cytoplasmic antibodies (pANCA) previously have been shown to be serum markers in dogs with chronic enteropathies, with dogs that have food‐responsive disease (FRD) having higher frequencies of seropositivity than dogs with steroid‐responsive disease (SRD). The indirect immunofluorescence (IIF) assay used in previous publications is time‐consuming to perform, with low interobserver agreement. Forty‐four dogs with FRD, 20 dogs with SRD, 20 control dogs, and 38 soft‐coated wheaten terrier (SCWT) or SCWT‐cross dogs

Comparative pharmacokinetic and cytotoxic analysis of three different formulations of mitoxantrone in mice.

Two liposomal formulations of mitoxantrone (MTO) were compared with the aqueous solution (free MTO) in terms of their pharmacokinetic behaviour in ICR mice and cytotoxic activity in a nude mouse xenograft model. The three different formulations of MTO [free MTO, phosphatidic acid (PA)-MTO liposomes, pH-MTO liposomes] were administered intravenously (three mice per formulation and time point) at a dose of 4.7 micromol kg(-1) for free MTO, 6.1 micromol kg(-1) for PA-MTO and 4.5 micromol kg(-1) for pH-MTO. The concentrations of MTO were determined using high-performance liquid chromatography (HPLC) in blood, liver, heart, spleen and kidneys of the mice. Additionally, the toxicity and anti-tumour activity of MTO was evaluated in a xenograft model using a human LXFL 529/6 large-cell lung carcinoma. The dose administered was 90% of the maximum tolerated dose (MTD) of the corresponding formulation (8.1 micromol kg(-1) for free MTO, 12.1 micromol kg(-1) for PA-MTO and pH-MTO). The pharmacokinetic behaviour of PA-MTO in blood was faster than that of free MTO, but the cytotoxic effect was improved. In contrast, pH-MTO showed a tenfold increased area under the curve (AUC) in blood compared with free MTO, without improvement of the cytotoxic effect. This discrepancy between the pharmacokinetic and cytotoxic results could be explained by the fact that MTO in pH-MTO liposomes remains mainly in the vascular space, whereas MTO in PA-MTO liposomes is rapidly distributed into deep compartments, even more so than free MTO

Direct observation of domain-wall configurations transformed by spin currents

Direct observations of current-induced domain-wall propagation by spin-polarized scanning electron microscopy are reported. Current pulses move head-to-head as well as tail-to-tail walls in sub-micrometer Fe_{20}Ni_{80} wires in the direction of the electron flow, and a decay of the wall velocity with the number of injected current pulses is observed. High-resolution images of the domain walls reveal that the wall spin structure is transformed from a vortex to a transverse configuration with subsequent pulse injections. The change in spin structure is directly correlated with the decay of the velocity.Comment: 5 pages, 3 figure

Absence of stable collinear configurations in Ni(001)ultrathin films: canted domain structure as ground state

Brillouin light scattering (BLS) measurements were performed for (17-120) Angstrom thick Cu/Ni/Cu/Si(001) films. A monotonic dependence of the frequency of the uniform mode on an in-plane magnetic field H was observed both on increasing and on decreasing H in the range (2-14) kOe, suggesting the absence of a metastable collinear perpendicular ground state. Further investigation by magneto-optical vector magnetometry (MOKE-VM) in an unconventional canted-field geometry provided evidence for a domain structure where the magnetization is canted with respect to the perpendicular to the film. Spin wave calculations confirm the absence of stable collinear configurations.Comment: 6 pages, 3 figures (text, appendix and 1 figure added

Superconducting Transition Temperature in Heterogeneous Ferromagnet-Superconductor Systems

We study the shift of the the superconducting transition temperature $T_c$ in ferromagnetic-superconducting bi-layers and in a superconducting film supplied a square array of ferromagnetic dots. We find that the transition temperature in these two cases change presumably in opposite direction and that its change is not too small. We extend these results to multilayer structures. We predict that rather small external magnetic field $\sim 10$ Oe can change the transition temperature of the bilayer by 10% .Comment: 9 pages, 2 figure

Stability of periodic domain structures in a two-dimensional dipolar model

We investigate the energetic ground states of a model two-phase system with 1/r^3 dipolar interactions in two dimensions. The model exhibits spontaneous formation of two kinds of periodic domain structure. A striped domain structure is stable near half filling, but as the area fraction is changed, a transition to a hexagonal lattice of almost-circular droplets occurs. The stability of the equilibrium striped domain structure against distortions of the boundary is demonstrated, and the importance of hexagonal distortions of the droplets is quantified. The relevance of the theory for physical surface systems with elastic, electrostatic, or magnetostatic 1/r^3 interactions is discussed.Comment: Revtex (preprint style, 19 pages) + 4 postscript figures. A version in two-column article style with embedded figures is available at http://electron.rutgers.edu/~dhv/preprints/index.html#ng_do

Behcet disease (BD) and BD-like clinical phenotypes : NF-kappa B pathway in mucosal ulcerating diseases

Behcet's disease (BD) is a heterogeneous multi-organ disorder in search of a unified pathophysiological theory and classification. The disease frequently has overlapping features resembling other disease clusters, such as vasculitides, spondyloarthritides and thrombophilias with similar genetic risk variants, namelyHLA-B*51,ERAP1,IL-10,IL-23R. Many of the BD manifestations, such as unprovoked recurrent episodes of inflammation and increased expression of IL-1, IL-6 and TNF alpha, overlap with those of the hereditary monogenic autoinflammatory syndromes, positioning BD at the crossroads between autoimmune and autoinflammatory syndromes. BD-like disease associates with various inborn errors of immunity, including familial Mediterranean fever, conditions related to dysregulated NF-kappa B activation (egTNFAIP3,NFKB1,OTULIN,RELA,IKBKG) and either constitutional trisomy 8 or acquired trisomy 8 in myelodysplastic syndromes. We review here the recent advances in the immunopathology of BD, BD-like diseases and the NF-kappa B pathway suggesting new elements in the elusive BD etiopathogenesis.Peer reviewe

Ferromagnetism and Temperature-Driven Reorientation Transition in Thin Itinerant-Electron Films

The temperature-driven reorientation transition which, up to now, has been studied by use of Heisenberg-type models only, is investigated within an itinerant-electron model. We consider the Hubbard model for a thin fcc(100) film together with the dipole interaction and a layer-dependent anisotropy field. The isotropic part of the model is treated by use of a generalization of the spectral-density approach to the film geometry. The magnetic properties of the film are investigated as a function of temperature and film thickness and are analyzed in detail with help of the spin- and layer-dependent quasiparticle density of states. By calculating the temperature dependence of the second-order anisotropy constants we find that both types of reorientation transitions, from out-of-plane to in-plane (``Fe-type'') and from in-plane to out-of-plane (``Ni-type'') magnetization are possible within our model. In the latter case the inclusion of a positive volume anisotropy is vital. The reorientation transition is mediated by a strong reduction of the surface magnetization with respect to the inner layers as a function of temperature and is found to depend significantly on the total band occupation.Comment: 10 pages, 8 figures included (eps), Phys Rev B in pres